Ive got a 24' Hawaiian daycruiser with a 454 and Berkeley jet.  the rpm range is around 600 to 5400.  I have  a motor that idles around 1500 and tops out around 7500.  What kind of performance difference would there be?  Changes I would have to do?  etc?

IMHO, it is not that simple.

You would really need to know what the torque curve looks like.

My immediate suspicion would be that in it's current configuration, it would never get to the rpm needed to get to the max numbers.

It is very likely the impeller would need to be trimmed in order to get to the RPM needed to really shine. Unless of course your talking a 900 HP animal.

Without more information on the build, or a very detailed dyno sheet, I am afraid your question is quite difficult to answer. A wild ass guess (WAG) could be made though.

Also. in a 24' tank, I would have a hard time believing even another 100 HP would make a huge difference speed wise.

GT

Ive got a 24' Hawaiian daycruiser with a 454 and Berkeley jet.  the rpm range is around 600 to 5400.  I have  a motor that idles around 1500 and tops out around 7500.  What kind of performance difference would there be?  Changes I would have to do?  etc?

My barge idles at ~1100 rpm or so, It will sit at 650, but there's not enough thrust for maneuvering around the docks, hence the 1100 r's.

Cutting the impeller down would get your (other) engine into the sweet spot, but is counter-productive for the thrust required to get that large hull on plane, and you'd get maybe 7500 r's @ 50 mph. I'm at 44-4600 @ 50 mph

I'd go with the biggest impeller you can (A2 Berk, AA A/T) and build the motor to suit the larger wheel.

You may just need to re-cam the motor to make it happy in the boat.

100 horses will give you better acceleration, not so much for top speed.


Dan'l